There are many types of known flow metering and measuring devices and they include the following. Mass flow meters utilize temperature sensors that are placed upstream and downstream of a heating coil. The mass flow rate is inversely proportional to the temperature difference between the sensors. These flow meters are designed primarily for metering gas flow.
Turbine flow meters utilize a flowtube that contains a small propeller, or turbine, mounted co-axially. The angular speed of the tube is equivalent to flow rate. These flow meters produce an electrical output proportional to turbine speed.
In positive displacement flow meters, fluid enters the flow sensor chamber forcing a piston to move. Piston motion is proportional to flow rate and the flow meter produces an output signal based on the frequency of piston motion.
In vortex transmitter flow meters, flow passes baffles inside a transmitter, causing vortices to form. The frequency of the vortices is directly proportional to flow rate. Vortices cause pressure fluctuations which are sensed, amplified, and converted to an output signal.
Doppler flow meters utilize an ultrasonic beam that is transmitted at an angle into a fluid to be metered. Impurities in the fluid reflect the beam at a slightly different frequency to a receiving sensor. The Doppler shift value is proportional to flow velocity.
In magnetic flow meters, movement of a conductive fluid through a magnetic field generates a signal proportional to velocity. This technique utilizes the Faraday principle.
In differential pressure flow meters, a pressure difference is measured across an orifice. Flow is proportional to this pressure difference.
Though these flow meters have had a beneficial impact on flow metering, they are disadvantageous for one or more of the following reasons. They present an undesirable high back pressure to the sensed fluid. They are sensitive to particulates in the fluid or they require high particulate concentration for the fluid to be measured. Air bubbles can effect the accuracy of flow rate determination or can block flow. Many of these sensors measure flow indirectly by measuring the velocity and hence may provide undesirably inaccurate flow rates. The cost of some of the sensors used in these systems is undesirably high.
A need thus exists for a flow measuring and metering devices that has low susceptibility or sensitivity to particulate levels, does not produce back pressure and is accurate and inexpensive to produce and use, amongst other features.